1. Field of the Invention
The invention relates to water-redispersible dispersion powder compositions comprising gemini surfactants, a process for producing them and their use in building materials, in particular in self-leveling flooring compositions and screeds.
2. Background Art
Polymers based on vinyl esters, vinyl chlorides, (meth)acrylate monomers, styrene, butadiene and ethylene are used in many applications, particularly in the form of their aqueous dispersions or water-redispersible polymer powders, for example as coating compositions or adhesives for a variety of substrates. In building compositions, for example those based on cement or gypsum plaster, dispersion powders stabilized with protective colloids are used to improve adhesion, abrasion resistance, scratch resistance or the tensile bending strength (Tonindustrie-Zeitung, 1985, 9, page 698). Such dispersion powders are described, for example, in DE-A 2049114 and are produced by spray drying aqueous polymer dispersions with addition of polyvinyl alcohol and further additives. Free-flowing powders having particle sizes of from 10 and 250 μm which can be obtained in this way redisperse in water to form dispersions having particle sizes of from 0.1 to 5 μm. Such redispersions have to remain stable over a relatively long period of time, i.e. they must not tend to settle, in order to be able to be used in the abovementioned applications.
An important field of use for dispersion powders is in hydraulically setting, self-leveling flooring compositions. Such flooring compositions are known from DE-A 3028559 and DE A 10061410 and generally comprise cement or mixtures of various cements, carefully matched filler combinations, dispersion powders, plasticizers and, if appropriate, further additives. The self-leveling flooring compositions are generally delivered to the building site as dry mortar, simply mixed with water on site, and applied to the floor. The applied layer spreads to give a smooth surface which serves either directly as a surface layer or as a substrate for further coatings. Problems can occur here, especially in the application of relatively thick layers. Unevennesses such as craters, pinholes or air inclusions are formed at the surface of the applied layer and represent points of attack for increased abrasion in use. Further treatment of the surface is necessary to alleviate these deficiencies.
To prevent the occurrence of such unevennesses, additives have hitherto been used. Thus, EP-A 477900 recommends the use of fully hydrolyzed copolymers of 1-alkylvinyl esters and vinyl esters. However, such additives are complicated to produce, which is a considerable economic disadvantage for corresponding dispersion powder formulations.
EP-B 1133456 describes an alternative route to a solution using a dispersion powder based on a vinylaromatic-1,3-diene polymer. However, the polymerization of these monomers forms volatile by-products (Diels-Alder compounds) which cannot be removed completely during the production process and are therefore liberated subsequently during use of the dispersion powders or the downstream products of the dispersion powders. This leads to severe odor pollution. This is a great disadvantage, especially in a large-area application such as flooring compositions.